1. Field of the Invention
This invention relates to a novel liquid level indicator which senses the height of a liquid level at a first location which is remote from a second location where the sensed height is indicated. In particular, this invention relates to a liquid level indicator which incorporates fiber optical signal transmission concepts.
2. Description of the Prior Art
During the recent years fiber optical signal transmission has become a significant technological innovation in electronic systems. Among the reasons for preference of fiber optical signal transmission to the former electric signal transmission is the availability of additional bandwidth combined with the elimination of electromagnetic interferences. Other reasons include the convenient separation of the electric potentials of various system components.
Fiber optical transmission has been used for medium and long distance communication and for digital data transmission in certain industry applications where electromagnetic interference or electric separation is of special significance. Fiber optical transmission lines have also been used in connection with high voltage switching, power plant control and process control of electric furnaces. The application in aircraft and in automobiles is also known.
In control systems signal communication in digital form is performed not only between data processing units, but also between data processing units and input and/or output devices. Special signal sensitivity exists between sensors and data processing devices. Therefore, fiber optical communication on a digital basis has been used for signal transmission between sensors and the control and/or processing system (Control Engineering, February 1979, pages 30-33). The sensor devices serve to acquire input information relative to physical parameters which are of significance for the control and/or processing system, such as temperature, pressure, position, flow, speed, level of a liquid, etc.
In the German Offenlegungsschrift No. 2,034,344, FIGS. 7a-7i, a liquid level indicator is disclosed which uses fiber optical signal transmission. In this prior art indicator, light passes through a curved fiber. When the bow or bend of the fiber is immersed into the liquid, the light within the fiber is no longer totally reflected in this region. The light transmitted through the fiber suffers a loss, the quantity of which is dependent upon the depth of immersion. The transmitted intensity may be measured by an electric light detector. Its output signal, that is an analog signal, may be further processed. The range of level height that can be measured with this prior art indicator is limited.
For many purposes it is desirable to have a digital or quasi-digital signal as indication signal for the depth of immersion or the height of the liquid level. In addition, it is desirable to design a liquid level indicator that can operate over a large range of levels.